Functional studies have revealed that the matrix protein (MA) of HIV-1 is critically involved in key steps of the replication cycle, including the intracellular localization of the Gag polyprotein, the incorporation of the viral envelope glycoprotein into virus particles and early post-entry events. Moreover, several lines of research indicate these roles may be dependent upon MA interacting with host proteins, yet little is known about the identity or role of these cellular co-factors. The goal of our proposed research is to identify one or more MA binding proteins critical for SIVcpz replication in chimpanzee cells. In our preliminary studies, we identified an adaptive change at amino acid 30 (MA30) in HIV-1 MA protein and subsequently showed that MA30 is a critical determinant for SIVcpz replication in chimpanzee, but not human, CD4+ T-lymphocytes. The observed differences in phenotype between wildtype and MA30 mutant SIVcpz viruses is likely due to the existence of a polymorphic MA binding factor in human and chimpanzee hosts. Specifically, we will: 1. Characterize the replication defect of SIVcpz MA30 mutants. We will determine which step of the SIVcpz life cycle is affected by the mutation at MA30 by comparing wildtype and mutant viruses in chimpanzee T-cell-based replication and virus particle release assays. We will also passage the SIVcpz MA30 mutants in chimpanzee cells to obtain revertants that replicate at levels comparable to wildtype virus. These studies will reveal whether other MA residues or other viral proteins cooperate with MA30. 2. To identify SIVcpz MA co-factor(s) in chimpanzee cells. We will use proteomics and mass spectrometry techniques to identify chimpanzee-specific cellular proteins that differentially bind to SIVcpz wildtype and MA30 mutant viruses. The goal of these studies is to discover novel MA-binding co-factors required for SIVcpz replication and define how these cellular proteins participate in the viral lifecycle. We anticipate that results from these studies will reveal new chemotherapeutic targets for agents that could prevent disease by blocking virus egress in HIV-1 infected patients. PUBLIC HEALTH RELEVANCE: The HIV-1 core protein, matrix (MA), is essential for viral replication because of it is implicated in the targeting and localization of the structural Gag protein to the site of virus particle assembly, the regulation the Env glycoprotein incorporation into budding virus particles and the control of early post-entry events. The goal of our proposed research is to identify one or more MA binding proteins critical for SIVcpz replication in chimpanzee cells. In our preliminary studies, we identified an adaptive change at amino acid 30 (MA30) in HIV-1 MA protein and subsequently showed that MA30 is a critical determinant for SIVcpz replication in chimpanzee, but not human cells. The knowledge gained from this project and the SIVcpz-chimpanzee model can be used to expand our understanding of HIV-1 MA protein interactions and could lead to new approaches for treatment of HIV-1 in patients.